JPS6376389A - Optical integrated element - Google Patents

Abstract

PURPOSE:To absorb efficiently incident light inside a crystal by forming a light receiving face of a photodetector so that it has an angle of polarization to the incident light coming from a semiconductor laser. CONSTITUTION:A groove 5 having a width of around 50mum is formed in a semiconductor laser element and its element permits one side of the laser to functions as the semiconductor laser 2 and other side to functions as a photodetector 3. And the groove 5 is vertically formed to an optical axis at the semiconductor laser 2 side and is used as a reflecting interface of the semiconductor laser 2. In such a case, when a relation of tan thetaB=b (constant), where thetaB is an angle of polarization toward materials of the photodetector, is valid, an output light out of the laser semiconductor laser 2 always comes at the angle of polarization toward a portion of the photodetector 3 and in principle its reflectance results in zero. Subsequently, the photodetector 3 can absorb efficiently an incident light coming from the semiconductor laser 2 inside a crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical integrated device, and particularly to an optical integrated device in which a semiconductor laser and a light receiving element are formed on the same semiconductor substrate.

(Prior Art) Compound semiconductor lasers with various structures are used as light sources for optical communications, etc., and in order to detect the optical output of such semiconductor lasers, a light receiving element is installed on the same substrate as the substrate on which the semiconductor laser is formed. An optical integrated element that can control the suitability of the light output of the semiconductor laser by detecting the light output of the semiconductor laser using the light receiving element is disclosed in the document ELECTRONIC LETTER.
3), 1980-4-24゜Vol, 16. A9
, pp. 342-343,
Proposed.

In a typical optical integrated device, a groove with a width of several tens of micrometers is formed by etching in a direction perpendicular to the resonator, and one of two diodes separated by this groove operates as a semiconductor radar and the other as a light receiving element. That is, by applying a forward bias to the former and a reverse bias to the latter, they can be operated as a semiconductor laser and a light receiving element, respectively.

In this configuration, since the semiconductor laser and the photodetector are fabricated on the same substrate, the overall size can be made smaller than when each is made up of separate elements, and the optical axis of the semiconductor laser and the photodetector are aligned. This has the advantage that positioning is not required.

Furthermore, in order to efficiently absorb incident light within the crystal of a normal light receiving element, an antireflection film is applied to the light receiving surface. (If there is no anti-reflection film, semiconductor devices such as InP generally have a reflection loss of about 30%.) (Problem to be solved by the invention) However, in the optical integrated device with the above configuration, the semiconductor laser and the light receiving element are separated by grooves having a width of several tens of micrometers, so it is difficult to form an antireflection film on the light receiving surface of the groove portion of the light receiving element. Therefore, there is a problem that the light receiving sensitivity is reduced.

In addition, reflected light from the light receiving surface causes deterioration of the characteristics of the semiconductor laser.

The object of the present invention is to eliminate the above-mentioned problem of reflection on the light receiving surface of a light receiving element and to provide a high-performance optical integrated element in which a semiconductor laser and a light receiving element are integrated on the same semiconductor substrate. .

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an optical integrated device in which a semiconductor laser and a monitoring light-receiving element are formed on the same semiconductor substrate. The light receiving surface is formed to form a Brewster angle with respect to the incident light from the semiconductor radar.

(Function) According to the present invention, as described above, a semiconductor laser and a light receiving element whose light receiving surface forms a Brewster angle with respect to the incident light from the semiconductor laser are formed on the same semiconductor substrate. Therefore, the output light from the semiconductor radar does not always enter the light receiving element portion at Brewster's angle, and the incident light can be efficiently absorbed within the crystal.

(Example) FIGS. 1(a) and 1(b) are a perspective view and a plan view, respectively, of an optical integrated device for explaining the present invention in detail,
This will be explained below using the drawings.

In FIG. 1(a), 1 is a compound semiconductor substrate such as InP, 2 is a semiconductor laser, 3 is a light receiving element for monitoring incident light from the semiconductor laser 2, 4 is an electrode, and 5 is a groove. A groove 5 having a width of about 50 μm as shown in FIG.
, the other is operated as the light receiving element 3. Here, the groove 5 is formed perpendicular to the optical axis of the laser on the side of the semiconductor laser 2 and is used as a reflection surface of the semiconductor laser 2. Further, the groove 5 on the light receiving element 3 side is etched so as to form a curve given by the following equation (1).

r=aebθ... (1) Here, Fig. 1 (
As shown in b), r is the distance from the emission point of the semiconductor laser, θ is the angle between the stripe direction of the semiconductor laser and the emitted light, and a and b are constants. At this time, assuming that the Brewster's angle with respect to the material of the photodetector is θ8, 10, = b... If the relationship (2) holds, the output light from the semiconductor laser 2 will always be incident on the photodetector 3 at the Brewster's angle. Therefore, in principle, the reflectance becomes 0. For example, if the light receiving part is InGaAsP (band gap 0.95 eV), the refractive index is 3.51.
, that is, b=3°51. At this time θ8=7
It becomes 4°. Etching at this time was performed using HCl:CHCOOH:H20□=1:2:1 as in the conventional case.
Etching at 15℃, washing with water,
A multi-stage etching method in which drying is repeated, a reactive ion etching method, a plasma etching method, etc. may be used.

As described above, according to the embodiment of the present invention, the semiconductor laser 2
In integrating the light-receiving element 3, whereas conventional grooves were cut perpendicular to the stripes of the semiconductor laser, grooves were cut perpendicularly to the semiconductor laser 2 side, and grooves were cut perpendicularly to the light-receiving element 3 side to the incident light.
Since the groove 5 is formed to form a star angle, the light receiving element 3 can efficiently absorb the incident light from the semiconductor laser 2 within the crystal. Further, according to the embodiments of the present invention, a conventional manufacturing method can be used, and a high-performance optical integrated device can be easily formed.

(Effects of the Invention) As described above, according to the structure of the present invention, reflection at the light-receiving part is eliminated, the sensitivity of the light-receiving element is improved, and characteristic deterioration of the semiconductor laser due to reflected light can be eliminated, and the semiconductor laser and the light-receiving element are It is possible to realize a high-performance optical integrated device that integrates these on the same substrate.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are a perspective view and a plan view, respectively, of an optical integrated device for detailed explanation of the present invention. 1... Compound semiconductor substrate, 2... Semiconductor laser, 3
... Light receiving element, 4... Electrode, 5... Groove. Patent applicant: Oki Electric Industry Co., Ltd. (a) @Figure 4 (b) Senwobe

Claims (1)

[Claims] In an optical integrated device in which a semiconductor laser and a light receiving element are formed on the same semiconductor substrate, the light receiving surface of the light receiving element forms a Brewster angle with respect to the incident light from the semiconductor laser. An optical integrated device characterized by being formed in.